The present invention concerns a device for measuring distortion in cylinders. It includes a sensor projecting straight out of the end of a motion-transmitting arm. The arm can be both translated and rotated. The sensor accommodates a probe that probes the geometry of the surface of the cylinder.
A device of this type is known from French A 1 544 088. A sensor is mounted on the end of a measurement arm and accommodates a geometry-probing pin. The arm executes translational motions. The sensor pivots around an axis extending across the axis of the arm, rotating the pin more than 300.degree. C. The rotation allows the pin to probe slotted cylindrical-surface geometries from the side once the arm with the sensor mounted on its head has been introduced through the slots paralleling the axis of the cylinder from the side into the cylindrical space being measured.
This known device, however, is totally unsuited for detecting cylinders with continuous surfaces. The present invention is intended to be inserted along the axis into a cylinder with a solid surface.
A device for this purpose is known form German Patent 3 024 331. It is intended for detecting distortion in cylindrical spaces. A measurement arm is introduced into the space and moved along its circumference. Mounted on the arm is a sensor that can execute translational motions along the axis of the arm. The sensor in turn accommodates a radial pin that probes the geometry of the inner surface of the cylinder being measured.
Although this known device has been proven for measuring distortions in cylinders and in particular in cylinders in internal-combustion engines, it is open to improvement in conjunction with the design of the sensor and its considerable radial extension.
The object of the present invention is accordingly a device for the aforesaid purpose that is simple and lacks external mechanisms for controlling the sensor.
With the aforesaid prior art as a point of departure, this object is attained in accordance with the invention by providing that the sensor comprises a distortion-measuring structure accommodated in the head of the surface-geometry probe and a chuck for axially secured and undeflected tensioning of the probe. The probe is an elongated geometry-probing pin. The structure is securely tensioned remote from the chuck in the vicinity of a structure-attachment section in the head. The structure includes at least one zone of attenuation between the chuck and the structure-attachment section. The zone of attenuation comprises a resilient section and a strain gauge.
Whereas the sensor in the device described in German Patent 3 024 331 travels along a rotating distortion-measuring arm, the device in accordance with the present invention features the head of a surface-geometry probe on the end of a translating and rotating motion-transmitting arm. A distortion-measuring structure is accommodated stationary in the head of the probe. The probe is a geometry-probing pin that extends out of the head. One end of the probe is accommodated in an appropriate chuck in the structure. The structure includes a zone of attenuation in the form of a resilient section. The zone of attenuation is between the probe-accommodating chuck and a structure-attachment section that ensures permanent attachment of the structure to the head of the probe.
One advantage of this embodiment of a distortion-measuring device is that the sensor is accommodated in the practically entirely enclosed head of the probe. One end of the geometry-probing pin is tensioned into an appropriate chuck in the distortion-measuring structure. The point at the other end of the pin engages the work surface that contains the distortions being measured. The pin will as it probes that surface execute minimal rotations around its point of tension and minimal translational measurement motions. Such motions can themselves generate deformations in the zone of attenuation in the from of a resilient section.
The distortion-measuring structure in one embodiment of the invention includes at least two separate resilient sections that operate at a right angle to each other. A structure of this type allows measurements to be taken along two perpendicular axes.
The distortion-measuring structure in accordance with the present invention can also of course be designed to allow measurements along three perpendicular axes. Such an embodiment will require in addition to the two resilient sections operating at a right angle to each other another resilient section operating at a right angle to the other two.
It will be practical for the zones of attenuation in the form of resilient sections in the distortion-measuring structure in accordance with the invention to be parallel springs. Parallel springs will allow especially precise guidance of the area of the structure that includes the probe-accommodating chuck.
The distortion-measuring structure in another important embodiment of the invention is in one piece. The zones of attenuation in this embodiment are obtained by removing material.
The one-piece distortion-measuring structure can be in the shape of a C, with two horizontals connected by an upright and with a structure-attachment section. The attachment section can project out of the end of one horizontal remote from the upright. The other horizontal can accommodate the chuck for securing the surface-geometry probe. The upright and/or the first horizontal can accommodate the zones of attenuation in the form of resilient sections.
The upright and or the one horizontal in the distortion-measuring structure in one sensible advanced version of this embodiment are penetrated by breaches in the vicinity of the zones of attenuation in the form of resilient sections, leaving edges in the form of leaf springs. The edges left in the form of leaf springs constitute the parallel springs.
It has been proven practical for the upright between the two horizontals in the distortion-measuring structure to be penetrated by two separated breaches at a right angle to each other.
The breach in the horizontal that connects the structure-attachment section to the upright in the distortion-measuring structure in another advanced version of the invention can be longer than the interval between the attachment section and the upright. This design will render the distortion-measuring device particularly sensitive at an angle to the measurement axes provided by the other resilient sections. This sensitivity can be increased even further if one incision extends into the upright and another into the structure-attachment section directly against the side of the leaf-spring like edge that demarcates the breach in the other horizontal.
Another important advanced version is characterized by a lever arm that extends parallel to at least one zone of attenuation in the distortion-measuring structure, is tensioned securely in the vicinity of one end of the zone of attenuation, and can be forced tight against another component of the structure at an angle to its length.
Such a lever arm will, depending on its tension allow limited preliminary deformation of the zones of attenuation and accordingly adjustment of the overall device. The lever arm can extend inside the upright and parallel with the zone of attenuation inside the upright and engage a tensioning screw at its free end. The tensioning screw will be accommodated in a threaded bore in an extension of one horizontal of the distortion-measuring structure. The lever arm can, however, also extend inside the distortion-measuring structure and parallel with the zone of attenuation in the horizontal that connects the upright of the distortion-measuring structure with its attachment section and be tensioned by a screw that engages its free end. In this case the tensioning screw will be accommodated in a threaded bore in an extension of the structure-attachment section paralleling the axis of the upright.
It will be obvious that within the scope of this advanced version one can also parallel the zone of attenuation in the upright and another can parallel the zone of attenuation in the horizontal that connects the structure-attachment section to the upright.
Another sensible advanced version is characterized in that the probe-accommodating chuck constitutes a rapid probe-replacement system comprising an extension that can be secured tight to one horizontal of the distortion-measuring structure, a base plate, a magnet in the center of the base plate, and a tensioning plate magnetically secured to the base plate. The probe is tensioned to the tensioning plate by known means.
Securing the tensioning plate to the base plate at three points has been demonstrated particularly practical. The three-point connection can comprise bearing balls accommodated in depressions in the tensioning plate distributed at intervals of 120.degree. C. around the circumference. Each ball can rest against the surface of a cone or prism or against a plane.